The present invention relates generally to light reflectors for exterior automotive lighting applications and more specifically to a multi-faceted light reflector for a headlamp having facets formed by differentially tilted parabolic cylinders.
Several methods are known for controlling the light distribution from a light reflector. In U.S. Pat. No. 4,825,343, a projector headlamp has a reflective surface with a series of minute planar face elements to direct light from a light source in front of the reflecting surface to a predetermined region on a shade. The shade masks a portion of the light output from the headlamp. The face elements are arranged in a series of adjacent vertical columns to form the reflective surface. Each face element in a vertical column is aimed at a common point on the shade.
The '343 patent has several embodiments which describe the mirrored surface as having distinct regions providing different light directing functions. The functions of some of the regions change drastically from their adjacent regions. These drastic changes in function generally result in either a discontinuity between adjacent vertical columns or a misdirection of light. One drawback to such a system is that light distribution cannot be precisely controlled since a shade must be employed to block out a portion of the light output from the bulb, i.e., light having an upward directional component. Another drawback to such a system is that discontinuities between the individual steps on the surface of the base structure surface promotes the buildup of reflective coating that is adhered to the surface during manufacturing by spraying, resulting in undesirable light scattering. Yet another drawback to such a projector type headlamp is that the light pattern is of such a shape that a convex lens must be employed to obtain a proper light distribution pattern.
U.S. Pat. No. 4,704,661 describes a multi-faceted headlamp reflector having distinct bending and spreading facets formed of right and simple parabolic sections. The parabolic facet size is a function of the amount of bending and spreading required. Because the parabolic section size is directly dependent on its light directing function, the overall package size is fixed which allows little flexibility in overall design. Another drawback to such a configuration is that distinct steps are formed by the bending and spreading facets. The stepped facets have the drawback that when the facets are sprayed with reflective coating, the reflective coating tends to build up on the corners of the edges of each step and cause an uncontrolled diffusion of the light.
A multifaceted design such as that disclosed in commonly assigned U.S. patent application Ser. No. 08/254,716, describes a reflective surface having facets whose shape is controlled to so that each facet edge aligns with the adjacent facet edge. For particular applications, the facet size must be made very small relative to the tooling. It has been found in the manufacture of the reflective surface that the size of the facets has a particular lower limit due to tooling tolerances and the smoothing effects of spraying a reflective coating over the surface. When the facets are made larger, tilting the facets in a horizontal or vertical direction does not yield desired results.
In automotive design, lighting engineers are typically given a package size to work within. Lighting engineers are increasingly given reduced package sizes while still having to maintain a required light distribution. It would therefore be desirable to provide a light reflector without having stepped surfaces to control the light output.